The present invention relates to a surveying instrument including a horizontal rotation driving unit with high accuracy and a simple structure.
A surveying instrument, e.g., a total station has a telescope unit for sighting a measuring point. The telescope unit is supported by a frame unit rotatably in a vertical direction, and further, the frame unit is supported rotatably in a horizontal direction by a base unit. Further, the total station includes a motor for rotating the telescope unit and a motor for rotating the frame unit.
Conventionally, a used motor is an electric motor. An output shaft of the electric motor and a rotation shaft of a rotation unit are connected via a first gear provided on the output shaft and a second gear provided on the rotation shaft and meshed with the first gear. Thereby, a mechanism is configured so that a rotating force of the electric motor is transmitted to the rotation unit via the first gear and the second gear. Further, there is a backlash in meshing between the first gear and the second gear. Since the backlash affects a rotational accuracy and a rotation positioning accuracy, the backlash needs to be made as small as possible. Particularly in a surveying instrument, an accuracy of a rotation angle is required by a unit of seconds. Thus, a highly accurate gear is needed, and further, high assembling accuracy is also required. For this reason, a manufacturing cost is high. Further, the backlash becomes large due to an abrasion of the gear or the like, and the accuracy is lowered over time.